Seasonal Variations in the Sources and Influential Factors of Aerosol Dissolved Black Carbon at a Southeast Coastal Site in China

Aerosols are a significant source of dissolved black carbon (DBC) in the ocean. However, how anthropogenic activities, including fossil fuel (FF) burning and human-initiated biomass burning (BB), would affect the seasonal variations in the concentration and condensation degree of aerosol DBC was not well constrained. To fill this knowledge gap, we collected 33 aerosol samples from December 2018 to September 2019 at a southeast coastal site in China. Concentrations of DBC, water-soluble organic carbon (WSOC), and elemental carbon (EC) were determined, and air quality data were collected. DBC concentration was 0.02–0.23 μgC m−3, with significantly higher values in spring and winter, and was affected by sources, rainfall frequency, and secondary processes. The source of DBC, as indicated by DBC/WSOC (range: 0.009–0.045) and DBC/EC (range: 0.007–0.065), was dominated by FF burning. Furthermore, the significantly higher DBC/WSOC value in late April to July indicated enhanced contribution from BB that was mainly associated with airmass transported from Southeast Asia (SEA). We further estimated that ∼30% of aerosol DBC was from BB from May to July. The condensation degree of DBC was variable, with significantly higher values in winter and spring, which might be associated with prolonged photo-dissolution. Significant correlations were also observed between DBC and PM10 and PM2.5, which might be utilized to estimate DBC deposition flux, albeit requiring more studies. Our study emphasized the influence of human activities (including BB activities) on atmospheric DBC deposition, which might affect the regional and even global DBC pools.